Year	Percent
1960	3.66685
1961	3.69125
1962	3.69299
1963	3.66246
1964	3.59239
1965	3.50648
1966	3.40469
1967	3.31679
1968	3.24541
1969	3.20865
1970	3.00616
1971	2.77024
1972	2.74673
1973	2.71432
1974	2.67901
1975	2.63417
1976	2.60113
1977	2.56776
1978	2.52198
1979	2.29626
1980	2.0303
1981	1.96862
1982	1.91683
1983	1.89841
1984	1.91057
1985	1.95007
1986	1.97182
1987	1.98004
1988	2.02481
1989	2.25132
1990	2.51055
1991	2.62732
1992	2.68725
1993	2.61569
1994	2.37761
1995	2.36272
1996	2.37064
1997	2.06244
1998	1.8251
1999	1.67748
2000	1.60236
2001	1.54285
2002	1.4876
2003	1.47142
2004	1.50024
2005	1.59498
2006	1.70234
2007	1.81575
2008	1.93988
2009	2.08502
2010	2.2303
2011	2.37925
2012	2.51054
2013	2.59292
2014	2.6098
2015	2.58582
2016	2.54601
2017	2.50731